LAKE FOREST>> There was a hostage situation within the halls of a middle school, and Tim Stack and Steve Lieberman were moving in.

They stood back to back, covering each other as they moved through the hallways and classrooms.

Children ran past screaming. Stack and Lieberman told them to take cover.

The two shuffled into a room, still covering each other’s backs, when the assailant emerged in front of Lieberman, holding a gun to a hostage’s head.

Lieberman called for the armed assailant to drop the gun. Instead, he aimed it at Lieberman, and Lieberman fired, killing the gunman and freeing the hostage along with the rest of the middle school students.

Lieberman and Stack managed to do all of this without firing a single bullet or leaving a Lake Forest warehouse. Welcome to Artemis Defense Institute, the only virtual defense training facility in the Southland.

Since Lieberman and his wife, Sandy, opened Artemis Defense Institute in April, the training facility has prepared 21 police and sheriff’s departments across Southern California, six of them in Los Angeles County, to use clear judgment in intense, fight-or-flight situations like an active shooter, as well as boost the confidence in about 500 private citizens learning how to properly handle a firearm.

“It’s really about perception and training,” said Stack, a Southern California law enforcement officer and instructor at Artemis Defense Institute. “It fully immerses you, where typical law enforcement training doesn’t.”

The Liebermans have worked against a reinvigorated gun control debate to get Artemis Defense Institute running, spurred by deadly shootings inside a movie theater in Aurora, Colo., an elementary school in Newtown, Conn., and the Sept. 16 shooting at the Navy Yard in Washington, D.C.

In a 5,760-square-foot warehouse at 11 Spectrum Pointe Drive in Lake Forest, Artemis Defense Institute uses three different high-definition, interactive systems for training, each worth about $500,000: A simple flat-screen monitor; a tri-fold, 180-degree system and the 300-degree, fully immersive system that Stack and Lieberman used during their school shooting scenario.

“It’s really a highly evolved Power Point presentation,” said co-owner Sandy Lieberman. “Our value in the business is not in our virtual machines, our value is in our instruction.”

Artemis Defense Institute was the result of a “compromise” between the Liebermans, Sandy said. Steve, an attorney and shooter since he was 8 years old, wanted to open a shooting range and gun education facility after his family’s plastics business closed. Sandy, never having any interest in guns before getting married, wanted to leave college entrance counseling, but remain in education.

Artemis has 65 interactive scenarios that participants can run through, including hostage and active shooter situations, and shooting ranges to improve marksmanship. Eventually, Artemis Defense Institute will incorporate its own custom footage and scenarios into the VirTra system, the Liebermans said.

A team of operators control the outcome of the scenario with computers, changing the situation based on the participant’s verbal communication with the simulator, as well as their body language and shooting accuracy. An advanced sound system also adds realistic gunfire sounds to enhance the experience.

“I know exactly what they need,” Stack said. “There’s a lot of things being thrown at a copper when they go in the field.”

The scenarios might not be real, but the guns used during the training are. They lock, load and fire, but you won’t find any bullets in the training warehouse. Instead, the barrels have been removed so no ammunition can be stored. They are loaded with CO2 canisters.

The guns have also been modified to interact with the scenario footage, so when a trainee aims at something and pulls the trigger, the video simulator reacts. Trainees can opt to wear Threat-Fire packs that will generate a small prick of electricity to simulate the consequences of getting shot. The packs can be set to shock for 30 milliseconds, or as long as 2.5 seconds.

“I thought it was shocking and disturbing, but it did as advertised,” Lt. Bret Parker said of the Threat-Fire packs. “It inoculated me to being in pain. As I continued to do training, I could fight through the pain.”

Parker, a lieutenant in the Courts Services Division of the Los Angeles County Sheriff’s Department, said he uses the VirTra simulations at Artemis Defense Institute at least once a week, sometimes with his adult son and daughter. The virtual school shooting scenario has prepared him should he ever find himself responding to such a situation, Parker said.

“It’s about as realistic as you’re going to get for that type of scenario training,” he said. “It was a more realistic, more comprehensive, and more stimulating shooting experience than going to the range.”

There are nine instructors at Artemis Defense Institute that work with both law enforcement officials and private citizens. That covers everything from the proper position of your hands and fingers on a gun — even when CO2 replaces bullets, your finger is never on the trigger until you’re absolutely ready to fire — and the proper stance when firing: knees slightly bent, chest slightly out.

“We work at their level,” said instructor Kyle Geenen. “The more realistic you treat it, the more it will trickle into real life.”

Of the 500 private citizens Artemis has taught to safely and properly shoot a gun, most have been women, the Liebermans said. Women rank as the fastest growing group of shooters, the Liebermans said.

When creating the business, the Liebermans wanted to have a female-friendly atmosphere since most shooting ranges are “dirty, with lots of testosterone,” Sandy Lieberman said.

“People who are practicing to get better, that alone is relaxing,” said Madison Morris, a female lab facilitator at Artemis and longtime shooter.

The training software has also been used for corporate team building and even bachelor parties, but guns are always pointed at the screens, and never at each other.

“That’s the difference between us and paint ball,” Sandy Lieberman said.

According to Steve Lieberman, training private citizens and law enforcement can reduced future shooting tragedies.